Many of the currently available surgical approaches for closing openings and repairing defects in anatomical lumens and tissues (e.g., blood vessels), septal defects, and other types of anatomical irregularities and defects are highly invasive. Surgical methods for clipping brain aneurysms, for example, require opening the skull, cutting or removing overlying brain tissue, clipping and repairing the aneurysm from outside the blood vessel, and then reassembling tissue and closing the skull. The risks related to anesthesia, bleeding, and infection associated with these types of procedures are high, and tissue that is affected during the procedure may or may not survive and continue functioning.
Minimally invasive techniques for treating aneurysms are accordingly highly desirable. In general, such minimally invasive therapeutic techniques help prevent material that collects or forms in the aneurysm cavity from entering the bloodstream and help prevent blood from entering and collecting in the aneurysm. This is often accomplished by introducing various materials and devices into the aneurysm. For example, implantable vaso-occlusive metallic structures are well known and commonly used. Many conventional vaso-occlusive devices have helical coils constructed from a shape memory material or noble metal that forms a desired coil configuration upon exiting the distal end of a delivery catheter. The function of the coil is to fill the space formed by an anatomical defect and to facilitate the formation of an embolus with the associated allied tissue. Multiple coils of the same or different structures may be implanted serially in a single aneurysm or other vessel defect during a procedure. Implantable framework structures are also used in an attempt to stabilize the wall of the aneurysm or defect prior to insertion of filling material such as coils. It is important to accurately implant vaso-occlusive devices within the internal volume of a cavity and to maintain the devices within the internal volume of the aneurysm. Migration or projection of a vaso-occlusive device from the cavity may interfere with blood flow or nearby physiological structures and can pose a serious health risk.
In addition to the difficulties of delivering implantable occlusion devices, some types of aneurysms are challenging to treat because of the particularities of the treatment site and/or the structural features of the aneurysm itself. Wide-neck aneurysms, for example, are known to present particular difficulty in the placement and retention of vaso-occlusive coils. Aneurysms at sites of vascular bifurcation are another example where the anatomical structure poses challenges to methods and devices that are effective in treating the typical sidewall aneurysms. It is therefore challenging to position conventional implantable devices during deployment, prevent shifting or migration of such devices after deployment, and preserve blood flow in neighboring vessels following deployment.